1. Field of the Invention
The present invention is directed to efficient one- or two-step processes for producing compositions enriched in phenols from dried or fresh plant material. More particularly, the present invention provides methods for producing compositions enriched for anthocyanins and proanthocyanins.
2. Description of the Prior Art
Anthocyanins are naturally occurring compounds that are responsible for the red, purple, and blue colors of many fruits, vegetables, cereal grains, and flowers. For example, the colors of berry fruits, such as blueberries, bilberries, strawberries, raspberries, boysenberries, marionberries, cranberries, are due to many different anthocyanins. Over 300 structurally distinct anthocyanins have been identified in nature. Because anthocyanins are naturally occurring, they have attracted much interest for use as colorants for foods and beverages.
Recently, the interest in anthocyanin pigments has intensified because of their possible health benefits as dietary antioxidants. For example, anthocyanin pigments of bilberries (Vaccinium myrtillus) have long been used for improving visual acuity and treating circulatory disorders. There is experimental evidence that certain anthocyanins and flavonoids have anti-inflammatory properties. In addition, there are reports that orally administered anthocyanins are beneficial for treating diabetes and ulcers and may have antiviral and antimicrobial activities. The chemical basis for these desirable properties of flavonoids is believed to be related to their antioxidant capacity. Thus, the antioxidant characteristics associated with berries and other fruits and vegetables have been attributed to their anthocyanin content.
Proanthocyanins are another class of flavonoid compounds that are found in fruits and vegetables and, while being colorless, have antioxidant activities.
Due to the above characteristics and benefits of anthocyanins and proanthocyanins, much effort has been put forth towards extracting these compounds from fruits, vegetables, and other plant sources. In addition to anthocyanins, plants, fruits, and vegetables also contain other compounds such as mineral salts, common organic acids such as citric or tartaric acid, carbohydrates, flavonoid glycosides and catechins. It is often desirable to isolate the anthocyanins and proanthocyanins from these compounds. Anthocyanins have been extracted from plants and fruits by various procedures. One extraction method of extracting anthocyanins employs sulfur dioxide. The extract is passed through an ion exchange column to adsorb the anthocyanin materials, and the adsorbed anthocyanins are eluted with acetone, alkali, or dimethyl formamide (DMF). Disadvantages of this process include the presence of sulfur dioxide, which interferes with adsorption of anthocyanins, thereby requiring multiple column adsorptions. Elution with alkali degrades the anthocyanins considerably, while DMF is not a recognized food additive and therefore complete removal of DMF from anthocyanins must be accomplished before the anthocyanins can be added to any food products.
Shrikhande, in U.S. Pat. No. 4,452,822, discloses a method for the production of a red coloring material for use as a colorant for food and beverages, wherein an anthocyanin-containing vegetable source material is extracted with sulfur dioxide to form an extract of anthocyanin material. The extract is first enzymatically treated to reduce or eliminate solid material present in the extract, and then treated by oxidizing the sulfur dioxide with hydrogen peroxide. After reducing the pH, the extract is loaded onto an ion exchange medium (a copolymer of styrene and divinyl benzene polymer or crosslinked polymethacrylate) that adsorbs the anthocyanins. However, it is very difficult to remove all the sulfur once it has been introduced. Further, hydrogen peroxide degrades the anthocyanins in the final product.
Gabetta, et al., in U.S. Pat. No. 5,200,186, disclose a process for the preparation of extracts with high content in anthocyanosides that involves treating a crude extract with bisulfite ions to provide anthocyanin-bisulfite adducts. After adjusting the pH of the extract to 5-6 by the addition of an aqueous alkali, the extract is loaded onto a non-polar polystyrene resin and the anthocyanin-bisulfite adducts are eluted. The obtained solution is extracted multiple times with butanol or amyl alcohol. After concentration and acidification (pH 1-2) of the organic phase, the extract with high anthocyanin content is isolated by lyophilization, or by precipitation with an aprotic solvent such as ethyl acetate. Again, it is difficult to remove all the sulfur once it has been introduced. In addition, it is difficult to remove the butanol, amyl alcohol, or ethyl acetate once these solvents are introduced.
Langston, in U.S. Pat. No. 4,500,556, discloses a method of producing an anthocyanin colorant from grape pomace by contacting an aqueous extraction solvent containing bisulfite ions to extract an anthocyanin-bisulfite ion adduct. The extract is then contacted with a nonionic adsorbent to adsorb the anthocyanin-bisulfite adduct, and the adsorbent is washed to remove soluble sugars, organic acids and other water soluble non-pigmented materials. The anthocyanins are then eluted from the adsorbent with an acidified organic solvent. Again, it is difficult to remove all the sulfur once it has been introduced.
Lietti, in U.S. Pat. No. 4,413,004, discloses a method of extracting anthocyanins from bilberry by extracting the fruit with anhydrous methanol containing hydrochloric acid, followed by adding lead acetate to precipitate the anthocyanins as the lead salts. However, the use of lead makes the products obtained by this process unsuitable for food use.
The above examples describe some processes known in the art for extracting and isolating anthocyanins from various plant materials. However, each of the above processes involves the use of toxic and/or environmentally hazardous materials. Consequently, the currant methods available for isolating and purifying anthocyanins are not easily scaled up to an efficient commercial process where disposal consideration of various chemicals and solvents play an important role in the overall feasibility of the process. Further, anthocyanins must be isolated in a manner which minimizes their natural instability toward degradation.
There is still a need, therefore, for an efficient process for isolating and purifying compositions containing anthocyanins for uses in nutraceuticals and pharmaceuticals that is cost-effective, scalable, economically sound, does not require the use of toxic solvents or reagents, and isolates the anthocyanins in a manner that minimizes their instability toward degradation.